1. The Field of the Invention
The present invention relates to methods and apparatus for using polarizing lenses or filters to create the perception of visual depth when viewing laterally moving objects in two dimensional single image displays and live scenes. In a further aspect, the present invention relates to the plane of polarization of polarizing filters used to produce the visual depth effects. In a still further aspect, the present invention relates to methods of controlling the movement of objects to create visual depth effects when observers wear glasses with polarizing lenses. The system is suited for motion picture films. The methods and apparatus may also be used for live scenes such as stage productions, video displays (television, computer displays, video games, etc.) and other types of media.
2. The Prior Art
The prior art includes methods to create the perception of depth in two-dimensional motion picture films and video displays. These methods have been described in or have been the subject of various patents. One class of prior art systems uses two separate shifted images to produce visual depth effects. These systems use special eye wear that transmits one image to the left eye and the other image to the right eye. When the special eye wear is worn by an observer, differences in the relative position of objects as seen by the two eyes produces the perception of depth. Observers viewing the imagery without the special glasses see double images.
The prior art commonly uses color or polarizing filters to separate the two images. When polarizing filters are used, light of the two images are polarized at right angles (90 degrees) to each other. Viewing glasses or spectacles with left and right eye polarizing filters with the plane of polarization at right angles to each other are used to transmit the image polarized in one plane to the left eye and the image polarized in the other plane to the right eye.
U.S. Pat. No. 4,957,361 to Shaw and U.S. Pat. No. 4,630,097 to Marks disclose systems using spectacles with left and right eye filters that are polarized at right angles to each other to produce the perception of depth when viewing motion pictures with double images that are polarized at right angles to each other. Numerous other prior art systems use viewing glasses with lenses polarized at right angles to each other in a similar manner to transmit one image to the left eye and another image to the right eye.
Another method of creating visual depth effects is based on the Pulfrich Effect. This effect is produced by viewing moving objects which appear brighter to one eye than the other. The standard Pulfrich Effect is commonly produced by placing a dark lens or filter over one eye. Objects that move laterally in one direction appear to be farther away from the observer. Conversely, objects that move laterally in the opposite direction appear to be closer to the observer. The standard Pulfrich Effect is a unidirectional motion sensitive depth effect. The relationship between the direction of movement and the perception of depth is dependent upon which eye is covered by the dark lens. When the left eye is covered by the dark lens, objects moving left to right (from the observer's perspective) appear to be farther away. Objects moving right to left appear to be closer. When the right eye is covered by the dark lens, objects moving left to right appear to be closer. Objects moving right to left appear to be farther away.
The apparatus used to produce the standard Pulfrich Effect tends to cause an undesirable side effect. The eye covered by the dark lens receives substantially less light than the other eye. This produces the sensation that the eye receiving less light is not working or dead. This dead eye effect becomes irritating to observers over time.
U.S. Pat. No. 3,445,153 to Marks is based on the standard Pulfrich Effect. Dudley discloses in U.S. Pat. No. 4,131,342 a method of combining the standard Pulfrich Effect with a chromostereoscopic effect. The chromostereoscopic effect is based on the finding that objects of colors towards the red end of the visual spectrum appear closer than objects of colors towards the blue end of the spectrum. The chromostereoscopic effect is very weak. It also restricts the use of colors in imagery. U.S. Pat. No. 4,131,342 teaches that the standard Pulfrich Effect is due to a "differential visual time-lag" whereby the human visual system processes a brighter image faster than a dimmer image. Therefore the location of moving objects appears to be different for the eye receiving the brighter image than for the eye receiving the dimmer image. The location of moving objects appears to be more advanced for the eye receiving the brighter image than for the eye receiving the dimmer image. This apparent eye to eye difference in the perceived location of moving objects produces the visual depth effect. U.S. Pat. No. 4,705,371 to Beard is also based on the standard Pulfrich Effect. Observers wear special lenses to reduce the dead eye effect. U.S. Pat. No. 4,836,647 to Beard discloses alternative colored filters to reduce the dead eye effect. The four methods above (U.S. Pat. Nos. 3,445,153; 4,131,342; 4,705,371; and 4,836,647) are all limited by the unidirectional nature of the standard Pulfrich Effect. They are all also somewhat prone to the dead eye effect.
U.S. Pat. No. 5,751,397 by Osgood teaches means of using colors to produce a bi-directional Pulfrich like effect. U.S. Pat. No. 5,751,397 uses objects moving laterally against colored backgrounds or surrounds, laterally moving colored objects, and colored viewing glasses. The left lens of the viewing glasses passes from 4 to 20 times as much light of one color (e.g. red) as the right lens. The right lens of the viewing glasses passes from 4 to 20 times as much light of another color (e.g. green). Objects moving laterally against surrounds of the first color, and laterally moving objects of the first color, appear closer to the observer when they move from left to right and farther away from the observer when they move from right to left. Objects moving laterally against surrounds of the second color, and laterally moving objects of the second color, appear closer to the observer when they move from right to left and farther away from the observer when they move from left to right.
The methods of U.S. Pat. No. 5,751,397 allow each eye to receive enough light to reduce or even totally avoid the dead eye effect. However, neither eye receives the full intensity of light across the entire visual spectrum. Therefore observers may perceive a reduction in the color saturation of the images viewed. The directionality of the depth effects is dependent upon the color of laterally moving objects and their surrounds. This limits the choice of colors in the imagery. It may also lead observers to use the colors of the laterally moving objects and their surrounds to predict the direction of the visual depth effects.
U.S. Pat. No. 5,886,771 by Osgood teaches means of using polarizing filters to produce a bi-directional Pulfrich like effect. A polarizing projection filter provides means to control the plane of polarization of projected imagery. The plane of polarization is changed by changing the orientation of the polarizing projection filter. An observer wears special viewing glasses with polarizing filters when viewing imagery polarized by the polarizing projection filter. The plane of polarization of the polarizing viewing filter for the right eye is rotated 30 degrees clockwise from horizontal. The plane of polarization of the polarizing viewing filter for the left eye is rotated 30 degrees counterclockwise from horizontal.
The imagery is projected onto a viewing screen which preserves the plane of polarization of the imagery light. When the polarizing projection filter has an angular offset of approximately 45 degrees clockwise from horizontal the projected imagery appears approximately 20 times brighter to an observer's right eye than to the observer's left eye. Objects moving laterally from right to left from the observer's perspective appear closer to the observer. Objects moving from left to right appear farther away from the observer. When the polarizing projection filter has an angular offset of approximately 45 degrees counterclockwise from horizontal the projected imagery appears approximately 20 times brighter to an observer's left eye than to the observer's right eye. Objects moving from right to left from the observer's perspective appear farther away from the observer. Objects moving from left to right appear closer to the observer.
The imagery for U.S. Pat. No. 5,751,397 can be viewed in full color. The dead eye effect can be avoided by periodically changing the plane of polarization of the polarizing projection filter. When the viewing screen used for U.S. Pat. No. 5,751,397 partially depolarizes the imagery light, the eye-to-eye brightness ratio is less than 20-to-1. This can reduce the strength of the perceived depth effects. The projection screens of certain movie theaters cause partial depolarization of the light of the projected imagery. This can reduce the strength of the perceived depth effects for U.S. Pat. No. 5,751,397 when these projection screens are used.